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Gentile JE, Corridon TL, Mortberg MA, D'Souza EN, Whiffin N, Minikel EV, Vallabh SM. Modulation of prion protein expression through cryptic splice site manipulation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.19.572439. [PMID: 38187635 PMCID: PMC10769280 DOI: 10.1101/2023.12.19.572439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
Lowering expression of prion protein (PrP) is a well-validated therapeutic strategy in prion disease, but additional modalities are urgently needed. In other diseases, small molecules have proven capable of modulating pre-mRNA splicing, sometimes by forcing inclusion of cryptic exons that reduce gene expression. Here, we characterize a cryptic exon located in human PRNP's sole intron and evaluate its potential to reduce PrP expression through incorporation into the 5' untranslated region (5'UTR). This exon is homologous to exon 2 in non-primate species, but contains a start codon that would yield an upstream open reading frame (uORF) with a stop codon prior to a splice site if included in PRNP mRNA, potentially downregulating PrP expression through translational repression or nonsense-mediated decay. We establish a minigene transfection system and test a panel of splice site alterations, identifying mutants that reduce PrP expression by as much as 78%. Our findings nominate a new therapeutic target for lowering PrP.
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Affiliation(s)
- Juliana E Gentile
- McCance Center for Brain Health and Department of Neurology, Massachusetts General Hospital, Boston, MA 02114
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142
| | - Taylor L Corridon
- McCance Center for Brain Health and Department of Neurology, Massachusetts General Hospital, Boston, MA 02114
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142
| | - Meredith A Mortberg
- McCance Center for Brain Health and Department of Neurology, Massachusetts General Hospital, Boston, MA 02114
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142
| | - Elston Neil D'Souza
- Big Data Institute and Centre for Human Genetics, University of Oxford, Oxford OX3 7LF, UK
| | - Nicola Whiffin
- Big Data Institute and Centre for Human Genetics, University of Oxford, Oxford OX3 7LF, UK
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA
| | - Eric Vallabh Minikel
- McCance Center for Brain Health and Department of Neurology, Massachusetts General Hospital, Boston, MA 02114
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142
| | - Sonia M Vallabh
- McCance Center for Brain Health and Department of Neurology, Massachusetts General Hospital, Boston, MA 02114
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA 02142
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2
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Bottorff TA, Park H, Geballe AP, Subramaniam AR. Translational buffering by ribosome stalling in upstream open reading frames. PLoS Genet 2022; 18:e1010460. [PMID: 36315596 PMCID: PMC9648851 DOI: 10.1371/journal.pgen.1010460] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 11/10/2022] [Accepted: 10/04/2022] [Indexed: 11/05/2022] Open
Abstract
Upstream open reading frames (uORFs) are present in over half of all human mRNAs. uORFs can potently regulate the translation of downstream open reading frames through several mechanisms: siphoning away scanning ribosomes, regulating re-initiation, and allowing interactions between scanning and elongating ribosomes. However, the consequences of these different mechanisms for the regulation of protein expression remain incompletely understood. Here, we performed systematic measurements on the uORF-containing 5' UTR of the cytomegaloviral UL4 mRNA to test alternative models of uORF-mediated regulation in human cells. We find that a terminal diproline-dependent elongating ribosome stall in the UL4 uORF prevents decreases in main ORF protein expression when ribosome loading onto the mRNA is reduced. This uORF-mediated buffering is insensitive to the location of the ribosome stall along the uORF. Computational kinetic modeling based on our measurements suggests that scanning ribosomes dissociate rather than queue when they collide with stalled elongating ribosomes within the UL4 uORF. We identify several human uORFs that repress main ORF protein expression via a similar terminal diproline motif. We propose that ribosome stalls in uORFs provide a general mechanism for buffering against reductions in main ORF translation during stress and developmental transitions.
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Affiliation(s)
- Ty A. Bottorff
- Basic Sciences Division and Computational Biology Program of the Public Health Sciences Division, Fred Hutchinson Cancer Center, Seattle, Washington, United States of America
- Biological Physics, Structure and Design Graduate Program, University of Washington, Seattle, Washington, United States of America
| | - Heungwon Park
- Basic Sciences Division and Computational Biology Program of the Public Health Sciences Division, Fred Hutchinson Cancer Center, Seattle, Washington, United States of America
| | - Adam P. Geballe
- Human Biology and Clinical Research Divisions, Fred Hutchinson Cancer Center, Seattle, Washington, United States of America
| | - Arvind Rasi Subramaniam
- Basic Sciences Division and Computational Biology Program of the Public Health Sciences Division, Fred Hutchinson Cancer Center, Seattle, Washington, United States of America
- Biological Physics, Structure and Design Graduate Program, University of Washington, Seattle, Washington, United States of America
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3
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Lee RE, Lewis CA, He L, Bulik-Sullivan EC, Gallant SC, Mascenik TM, Dang H, Cholon DM, Gentzsch M, Morton LC, Minges JT, Theile JW, Castle NA, Knowles MR, Kimple AJ, Randell SH. Small molecule eRF3a degraders rescue CFTR nonsense mutations by promoting premature termination codon readthrough. J Clin Invest 2022; 132:154571. [PMID: 35900863 PMCID: PMC9479597 DOI: 10.1172/jci154571] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 07/26/2022] [Indexed: 11/22/2022] Open
Abstract
The vast majority of people with cystic fibrosis (CF) are now eligible for CF transmembrane regulator (CFTR) modulator therapy. The remaining individuals with CF harbor premature termination codons (PTCs) or rare CFTR variants with limited treatment options. Although the clinical modulator response can be reliably predicted using primary airway epithelial cells, primary cells carrying rare CFTR variants are scarce. To overcome this obstacle, cell lines can be created by overexpression of mouse Bmi-1 and human TERT (hTERT). Using this approach, we developed 2 non-CF and 6 CF airway epithelial cell lines, 3 of which were homozygous for the W1282X PTC variant. The Bmi-1/hTERT cell lines recapitulated primary cell morphology and ion transport function. The 2 F508del-CFTR cell lines responded robustly to CFTR modulators, which was mirrored in the parent primary cells and in the cell donors’ clinical response. Cereblon E3 ligase modulators targeting eukaryotic release factor 3a (eRF3a) rescued W1282X-CFTR function to approximately 20% of WT levels and, when paired with G418, rescued G542X-CFTR function to approximately 50% of WT levels. Intriguingly, eRF3a degraders also diminished epithelial sodium channel (ENaC) function. These studies demonstrate that Bmi-1/hTERT cell lines faithfully mirrored primary cell responses to CFTR modulators and illustrate a therapeutic approach to rescue CFTR nonsense mutations.
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Affiliation(s)
- Rhianna E Lee
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Catherine A Lewis
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Lihua He
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Emily C Bulik-Sullivan
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Samuel C Gallant
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Teresa M Mascenik
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Hong Dang
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Deborah M Cholon
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Martina Gentzsch
- Department of Pediatrics, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Lisa C Morton
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - John T Minges
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | | | - Neil A Castle
- Research and Development, Icagen, Durham, United States of America
| | - Michael R Knowles
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Adam J Kimple
- Department of Otolaryngology, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
| | - Scott H Randell
- Marsico Lung Institute/Cystic Fibrosis Research Center, University of North Carolina at Chapel Hill, Chapel Hill, United States of America
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Baradaran-Heravi A, Balgi AD, Hosseini-Farahabadi S, Choi K, Has C, Roberge M. Effect of small molecule eRF3 degraders on premature termination codon readthrough. Nucleic Acids Res 2021; 49:3692-3708. [PMID: 33764477 PMCID: PMC8053119 DOI: 10.1093/nar/gkab194] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 03/04/2021] [Accepted: 03/10/2021] [Indexed: 12/16/2022] Open
Abstract
Premature termination codon (PTC) readthrough is considered a potential treatment for genetic diseases caused by nonsense mutations. High concentrations of aminoglycosides induce low levels of PTC readthrough but also elicit severe toxicity. Identifying compounds that enhance PTC readthrough by aminoglycosides or reduce their toxicity is a continuing challenge. In humans, a binary complex of eukaryotic release factors 1 (eRF1) and 3 (eRF3a or eRF3b) mediates translation termination. They also participate in the SURF (SMG1-UPF1-eRF1-eRF3) complex assembly involved in nonsense-mediated mRNA decay (NMD). We show that PTC readthrough by aminoglycoside G418 is considerably enhanced by eRF3a and eRF3b siRNAs and cereblon E3 ligase modulators CC-885 and CC-90009, which induce proteasomal degradation of eRF3a and eRF3b. eRF3 degradation also reduces eRF1 levels and upregulates UPF1 and selectively stabilizes TP53 transcripts bearing a nonsense mutation over WT, indicating NMD suppression. CC-90009 is considerably less toxic than CC-885 and it enhances PTC readthrough in combination with aminoglycosides in mucopolysaccharidosis type I-Hurler, late infantile neuronal ceroid lipofuscinosis, Duchenne muscular dystrophy and junctional epidermolysis bullosa patient-derived cells with nonsense mutations in the IDUA, TPP1, DMD and COL17A1 genes, respectively. Combination of CC-90009 with aminoglycosides such as gentamicin or ELX-02 may have potential for PTC readthrough therapy.
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Affiliation(s)
- Alireza Baradaran-Heravi
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Aruna D Balgi
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Sara Hosseini-Farahabadi
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Kunho Choi
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
| | - Cristina Has
- Department of Dermatology, Medical Center-University of Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Michel Roberge
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
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Becker JP, Helm D, Rettel M, Stein F, Hernandez-Sanchez A, Urban K, Gebert J, Kloor M, Neu-Yilik G, von Knebel Doeberitz M, Hentze MW, Kulozik AE. NMD inhibition by 5-azacytidine augments presentation of immunogenic frameshift-derived neoepitopes. iScience 2021; 24:102389. [PMID: 33981976 PMCID: PMC8082087 DOI: 10.1016/j.isci.2021.102389] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Revised: 03/11/2021] [Accepted: 03/30/2021] [Indexed: 12/22/2022] Open
Abstract
Frameshifted protein sequences elicit tumor-specific T cell-mediated immune responses in microsatellite-unstable (MSI) cancers if presented by HLA class I molecules. However, their expression and presentation are limited by nonsense-mediated RNA decay (NMD). We employed an unbiased immunopeptidomics workflow to analyze MSI HCT-116 cells and identified >10,000 HLA class I-presented peptides including five frameshift-derived InDel neoepitopes. Notably, pharmacological NMD inhibition with 5-azacytidine stabilizes frameshift-bearing transcripts and increases the HLA class I-mediated presentation of InDel neoepitopes. The frameshift mutation underlying one of the identified InDel neoepitopes is highly recurrent in MSI colorectal cancer cell lines and primary patient samples, and immunization with the corresponding neoepitope induces strong CD8+ T cell responses in an HLA-A∗02:01 transgenic mouse model. Our data show directly that pharmacological NMD inhibition augments HLA class I-mediated presentation of immunogenic frameshift-derived InDel neoepitopes thus highlighting the clinical potential of NMD inhibition in anti-cancer immunotherapy strategies.
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Affiliation(s)
- Jonas P. Becker
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Pediatric Oncology, Hematology and Immunology, Heidelberg University, 69120 Heidelberg, Germany
- Hopp Children's Cancer Center, National Center for Tumor Diseases (NCT), 69120 Heidelberg, Germany
| | - Dominic Helm
- Genomics and Proteomics Core Facility, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Mandy Rettel
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Frank Stein
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Alejandro Hernandez-Sanchez
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Applied Tumor Biology, Institute of Pathology, Heidelberg University, 69120 Heidelberg, Germany
- Collaboration Unit Applied Tumor Biology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Katharina Urban
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Applied Tumor Biology, Institute of Pathology, Heidelberg University, 69120 Heidelberg, Germany
- Collaboration Unit Applied Tumor Biology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Johannes Gebert
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Applied Tumor Biology, Institute of Pathology, Heidelberg University, 69120 Heidelberg, Germany
- Collaboration Unit Applied Tumor Biology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Matthias Kloor
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Applied Tumor Biology, Institute of Pathology, Heidelberg University, 69120 Heidelberg, Germany
- Collaboration Unit Applied Tumor Biology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Gabriele Neu-Yilik
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Pediatric Oncology, Hematology and Immunology, Heidelberg University, 69120 Heidelberg, Germany
- Hopp Children's Cancer Center, National Center for Tumor Diseases (NCT), 69120 Heidelberg, Germany
| | - Magnus von Knebel Doeberitz
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Applied Tumor Biology, Institute of Pathology, Heidelberg University, 69120 Heidelberg, Germany
- Collaboration Unit Applied Tumor Biology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Matthias W. Hentze
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
| | - Andreas E. Kulozik
- Molecular Medicine Partnership Unit (MMPU), Heidelberg University, 69120 Heidelberg, Germany
- European Molecular Biology Laboratory (EMBL), 69117 Heidelberg, Germany
- Department of Pediatric Oncology, Hematology and Immunology, Heidelberg University, 69120 Heidelberg, Germany
- Hopp Children's Cancer Center, National Center for Tumor Diseases (NCT), 69120 Heidelberg, Germany
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6
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Disrupting upstream translation in mRNAs is associated with human disease. Nat Commun 2021; 12:1515. [PMID: 33750777 PMCID: PMC7943595 DOI: 10.1038/s41467-021-21812-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 02/12/2021] [Indexed: 12/04/2022] Open
Abstract
Ribosome-profiling has uncovered pervasive translation in non-canonical open reading frames, however the biological significance of this phenomenon remains unclear. Using genetic variation from 71,702 human genomes, we assess patterns of selection in translated upstream open reading frames (uORFs) in 5’UTRs. We show that uORF variants introducing new stop codons, or strengthening existing stop codons, are under strong negative selection comparable to protein-coding missense variants. Using these variants, we map and validate gene-disease associations in two independent biobanks containing exome sequencing from 10,900 and 32,268 individuals, respectively, and elucidate their impact on protein expression in human cells. Our results suggest translation disrupting mechanisms relating uORF variation to reduced protein expression, and demonstrate that translation at uORFs is genetically constrained in 50% of human genes. The significance of translated upstream open reading frames is not well known. Here, the authors investigate genetic variants in these regions, finding that they are under high evolutionary constraint and may contribute to disease.
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Raxwal VK, Simpson CG, Gloggnitzer J, Entinze JC, Guo W, Zhang R, Brown JWS, Riha K. Nonsense-Mediated RNA Decay Factor UPF1 Is Critical for Posttranscriptional and Translational Gene Regulation in Arabidopsis. THE PLANT CELL 2020; 32:2725-2741. [PMID: 32665305 PMCID: PMC7474300 DOI: 10.1105/tpc.20.00244] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 06/23/2020] [Accepted: 07/08/2020] [Indexed: 05/19/2023]
Abstract
Nonsense-mediated RNA decay (NMD) is an RNA control mechanism that has also been implicated in the broader regulation of gene expression. Nevertheless, a role for NMD in genome regulation has not yet been fully assessed, partially because NMD inactivation is lethal in many organisms. Here, we performed an in-depth comparative analysis of Arabidopsis (Arabidopsis thaliana) mutants lacking the NMD-related proteins UPF3, UPF1, and SMG7. We found different impacts of these proteins on NMD and the Arabidopsis transcriptome, with UPF1 having the biggest effect. Transcriptome assembly in UPF1-null plants revealed genome-wide changes in alternative splicing, suggesting that UPF1 functions in splicing. The inactivation of UPF1 led to translational repression, as manifested by a global shift in mRNAs from polysomes to monosomes and the downregulation of genes involved in translation and ribosome biogenesis. Despite these global changes, NMD targets and mRNAs expressed at low levels with short half-lives were enriched in the polysomes of upf1 mutants, indicating that UPF1/NMD suppresses the translation of aberrant RNAs. Particularly striking was an increase in the translation of TIR domain-containing, nucleotide binding, leucine-rich repeat (TNL) immune receptors. The regulation of TNLs via UPF1/NMD-mediated mRNA stability and translational derepression offers a dynamic mechanism for the rapid activation of TNLs in response to pathogen attack.
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Affiliation(s)
- Vivek K Raxwal
- Central European Institute of Technology, Masaryk University, 625 00 Brno, Czech Republic
| | - Craig G Simpson
- Cell and Molecular Sciences, James Hutton Institute, Dundee DD2 5DA, United Kingdom
| | | | - Juan Carlos Entinze
- Division of Plant Sciences, University of Dundee at the James Hutton Institute, Dundee DD2 5DA, United Kingdom
| | - Wenbin Guo
- Information and Computational Sciences, James Hutton Institute, Dundee DD2 5DA, United Kingdom
| | - Runxuan Zhang
- Information and Computational Sciences, James Hutton Institute, Dundee DD2 5DA, United Kingdom
| | - John W S Brown
- Cell and Molecular Sciences, James Hutton Institute, Dundee DD2 5DA, United Kingdom
- Division of Plant Sciences, University of Dundee at the James Hutton Institute, Dundee DD2 5DA, United Kingdom
| | - Karel Riha
- Central European Institute of Technology, Masaryk University, 625 00 Brno, Czech Republic
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CTELS: A Cell-Free System for the Analysis of Translation Termination Rate. Biomolecules 2020; 10:biom10060911. [PMID: 32560154 PMCID: PMC7356799 DOI: 10.3390/biom10060911] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Revised: 05/29/2020] [Accepted: 06/13/2020] [Indexed: 12/11/2022] Open
Abstract
Translation termination is the final step in protein biosynthesis when the synthesized polypeptide is released from the ribosome. Understanding this complex process is important for treatment of many human disorders caused by nonsense mutations in important genes. Here, we present a new method for the analysis of translation termination rate in cell-free systems, CTELS (for C-terminally extended luciferase-based system). This approach was based on a continuously measured luciferase activity during in vitro translation reaction of two reporter mRNA, one of which encodes a C-terminally extended luciferase. This extension occupies a ribosomal polypeptide tunnel and lets the completely synthesized enzyme be active before translation termination occurs, i.e., when it is still on the ribosome. In contrast, luciferase molecule without the extension emits light only after its release. Comparing the translation dynamics of these two reporters allows visualization of a delay corresponding to the translation termination event. We demonstrated applicability of this approach for investigating the effects of cis- and trans-acting components, including small molecule inhibitors and read-through inducing sequences, on the translation termination rate. With CTELS, we systematically assessed negative effects of decreased 3′ UTR length, specifically on termination. We also showed that blasticidin S implements its inhibitory effect on eukaryotic translation system, mostly by affecting elongation, and that an excess of eRF1 termination factor (both the wild-type and a non-catalytic AGQ mutant) can interfere with elongation. Analysis of read-through mechanics with CTELS revealed a transient stalling event at a “leaky” stop codon context, which likely defines the basis of nonsense suppression.
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